together, when subtracted from the total sulphur dioxide, give that existing
as normal sulphite.
Commercial solid sodium bisulphite, sometimes called also Metasulphite or
Pyrosulphite (see Potassium bisulphite), usually contains 60-62% of total SO ;
the solution of 38-40° Baume contains 24-25%.
Na8CO8 = 106 ; Na2C03 + ioH20 = 286
This is sold as : Crude sodium carbonate (Crude soda], in more or less
coloured, crystalline masses, contaminated by chlorides, sulphates, sulphides,
thiocyanates, phosphates, silica, heavy and earthy metals and sodium
hydroxide ; Crystallised carbonate (Soda crystals] with 10 mols. of water,
containing particularly sulphates and chlorides but not in large proportions ;
Dry carbonate (Calcined soda or Soda ash] in white powder or masses, which
may contain sulphate, sulphide and hydroxide if made by calcination of
Leblanc soda, or chloride and bicarbonate, if it is Solvay or ammonia soda.
There is also pure sidiwn carbonate (crystallised or dry), which should be
free from impurities.
The analysis of sodium carbonate includes the qualitative investigation
of the various impurities (tests 1-14), to be made particularly on the pure
and chemically pure products ; and the determination of the water, titre
and some of the commoner impurities, especially with commercial sodas
(15-17). The quantities given for tests 1-9 refer to the crystallised car-
bonate ; one-third as much of the anhydrous carbonate should be taken.
1. Solubility.—i gram in 10 c.c. of water should give a clear solution.
2. Sulphates, Chlorides.—5 grams, dissolved in a slight excess of
dilute nitric acid and the solution made up to 25 c.c. with water, are tested
with barium chloride in the hot—examining after standing for 12 hours
(sulphates]—or with silver nitrate (chlorides].
3. Nitrates.—See Caustic Potash.
4. Phosphates .—20 grams dissolved in dilute nitric acid are treated
with ammonium molybdatc at a gentle heat.
5. Silica.—20 grams are dissolved in dilute hydrochloric acid and
evaporated on a steam-bath, the residue being dried at 105° and taken up
in water : the solution, thus obtained should be clear and should not deposit
flocks even after long standing.
6. Arsenic.—The solution is tested in the Marsh apparatus for one hour.
7. Alumina.—10 grams dissolved in 50 c.c. of water are acidified with
acetic acid, and then rendered alkaline with ammonia : any formation of
gelatinous flocks after long standing is noted.
8. Heavy Metals.—10 grams are dissolved in water (50 c.c.), acidified
with dilute hydrochloric acid and treated with hydrogen sulphide: no
change should occur even after addition of ammonia in excess.
9. Potassium.—3 grams, dissolved in dilute hydrochloric acid, are
treated with a few drops of platinic chloride and the liquid evaporated on
a steam-bath ; the dry residue should give a clear solution in 50 c.c. of 80%
alcohol. c.c. of cold boiled water without